The present invention generally relates to heating apparatus and, in an illustrated embodiment thereof, more particularly relates to a fuel-fired heating apparatus having a specially designed staged fuel burner system incorporated therein.
Multiple burner combustion systems are commonly utilized in a variety of fuel-fired heating appliances such as water heaters, pool heaters and boilers. In this type of combustion system, a plurality of mutually spaced apart, parallel, horizontally oriented tubular burners are disposed in a combustion chamber portion of the heating appliance. Each burner is typically of the “premix” type in which, during firing thereof, fuel from a source thereof, and fan-supplied primary combustion air are flowed through the tube to form therein a fuel/air mixture which is discharged through burner outlet openings and combusted without the use of secondary combustion air.
Many multiple burner combustion systems of this type are operated in a “staged” manner in which for low heating loads only some of the burners are fired, with the remaining burners remaining in an unfired state. When the heating load increases, some or all of the remaining burners are also fired to correspondingly increase the heating capability of the appliance. Conventional multiple burner combustion systems of this general type have associated therewith a variety of well known problems, limitations and disadvantages.
For example, when only some of the burners are being fired, uncombusted fuel being discharged from the firing burners tends to undesirably circulate under the unfired burners, and then is discharged from the heating apparatus, resulting in poor overall fuel combustion which is undesirable from an environmental emission standpoint. Further, during firing of a given burner of this type, a substantial temperature differential exists between the (hotter) top side of the burner and its (cooler) bottom side. This temperature difference causes differential longitudinal expansion of the burner during firing, thereby subjecting the burner to a substantial amount of thermal stress during its operation. Additionally, under certain operating conditions, the burners may harmonically resonate—a condition which undesirably increases the operating noise level of the appliance.
As can readily be seen from the foregoing, it would be desirable to provide in a fuel-fired heating appliance a multiple burner combustion system in which the above mentioned burner-related problems, limitations and disadvantages are eliminated or at least substantially reduced.